Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$19.60	11.474%	$21.8489	$21.85	$21.85	$21.80
Purchase #2	$173.56	9.184%	$189.4998	$189.50	$189.50	$189.50
Purchase #3	$121.61	4.650%	$127.2649	$127.26	$127.25	$127.30
Purchase #4	$158.30	8.668%	$172.0214	$172.02	$172.00	$172.00
Purchase #5	$62.67	3.342%	$64.7644	$64.76	$64.75	$64.80
Purchase #6	$129.79	13.424%	$147.213	$147.21	$147.20	$147.20
Purchase #7	$126.77	11.566%	$141.4322	$141.43	$141.45	$141.40
7 purchase totals =	$792.30		$864.0446	$864.03	$864.00	$864.00